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Reissue-d May 28, 1929.

Re. 17,309 PATENT OFFICE.

ARTHUR O. ZIMMERMAN, OF DAYTON, OHIO, ASSIGNOR TO THE DOW CHEMICAL COM- PANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN.

TREATMENT'OF MAGNESIUM AND MAGNESIUM ALLOYS TO INHIBIT CORROSION.

1T0 Drawing. Original No. 1,677,667, dated July 17, i928, Serial No. 747,128, filed October 31, 1924.

Application for reissue filed March 9, 1929. Serial No. 345,879.

other borates of the alkali metals, a coating.

or impregnation of phosphate, borate, or other compound of magnesium likely to form under the treatment, is produced. It is also desirable to have present in the treating. solution, an oxidizing salt such as manganese dioxide. As an example of a treatment which affords ample protection, the following is submitted: The material is immersed in a .7 5

per cent by volume solution of phosphoric acid, containing about 1 ounce of manganese. dioxide per gallon of solution. At the time the metal is immersed the solution should be heated to about 200 Fahrenheit, and this I 7 temperature maintained after the immersion of the metal, which remains immersed until a continuous coating or impregnation or the dark gray colored compound of magnesium is formed, or until practically all gas ceases to be evolved from this solution. Usually about one and one-half hours are suflicient for the complete treatment of the metal in the solution.

The metal is then removed from the solution and washed with water. After the washing with water, it is heat-treated by placing it in an oven. After baking for a short time, sufliciently to thoroughly dry and stabilize the coating, it is removed and cooled to room temperature. Subsequently a coating or coatings of paint, enamel or lacquer, or combinations thereofare applied, depending upon the results desired. It has been found that, for inhibiting corrosion when exposed to the atmosphere, salt water, benzol or gasoline, two coatin s of bakelite lacquer serve the purpose exce lently as a finishing coating material.

Although the protection alforded' by subsequent heat treating and painting is greatly improved, these two steps are not absolutely essential in the treatment of the metal. Very" good results are obtained by merel subjecting the metal to the action of the p osphoric acid,bpric acid or borax as the case may be,

and merely washing or drying the treated metal.

- It is essential that the solution of acid used be sufficiently weak so as to prevent too rapid action on the metal. In case the acid is stronger than it should be, the acid eats into the metal so rapidly that the scale or protective coating is loosened and does not rigidly adhere to the product. It has been found that a to a l per cent solution of phosphoric acid is most desirable, but if the time is increased considerably, a weaker solution than to l per cent may be used. Similarly it is possible to use more than a 1 per cent solution of phosphoric acid for a shorter period of time, although in such case the protective coating is not quite as integral as the coating which would be produced more slowly.

When boric acid is used in place of phosphoric acid as the treating acid, the solution should be slightly stronger than 1 per cent, as the boric acid is notquite so active an agent in attacking magnesium. \Less than a 5 per cent solution however should be used. In the case of borax, it has been found that less than a 5 per cent solution should be used for the best results, but this salt also may be slightly 7 stronger than the solution 01 phosphoric acid used. 1

The salts formed on the surface of the magnesium article treated are of an insoluble character and are quite stable and serve to adequately protect the material beneath it. They also form a surface to which the paintor lacquer may be effectively applied.

I claim 2 1. The method of treating magnesium and magnesium base alloys to inhibit corrosion, comprising treating the metal with a solution of not more than five per cent phosphoric acid, containing from one tenth to ten ounces manganesedioxide per gallon of solution for about one and one-half hours.

' 2. The method of treating magnesium and magnesium base alloys to inhibit corrosion, comprising treating the metal with a solution of not more than five per cent phosphoric acid,

3. The method of treating magnesium and' magnesium basealloys to inhibitcorrosion against natural and prepared agencies, comprising treating the metal with a solution of not more than five per cent phosphoric acid, until a coatin and impregnation of a magnesium phosp ate is formed on the surface .of the metal and subsequently drying the treated metal and coating with paint 'or lacquer. i n 4. The method of treating magnesium articles comprising treating the article in a water solution of less than 5 per cent of phosphoric acid, for about one and one-half hours at about 200 Fahrenheit in the presence of from one-tenth to ten ounces manganese dioxide per gallon of solution and subsequently drying the article.

5. The method of treating magnesium and magnesium base alloys to inhibit corrosion,

into a compound of magnesium containing phosphorus, by surface-treating such magnesium or magnesium alloy with a phosphorus-containing agent.

7. A-magnesium or magnesium alloy article provided with a closely adhering surface coating of a phosphorus compound formed in place by the inter-action of the magnesium and phosphorus compound.

8. A magnesium or magnesium alloy article provided with a closely adhering surface layer of a magnesium-phosphoruscompound formed in place by the inter-action of the magnesium and an agent containing a phosphoric radical.

.9. A magnesium ormagnesinin alloy article provided .with a closely adhering surface layer of magnesium phosphate, said layer be-i ing formed in place by the inter-action oi the magnesium and an agent containing the phosphoric acid. I

In testimony whereof I aflix my signature.

ARTHUR o. ZIMMERMAN. 

